An empirical study on DOACROSS loops

Loop-iteration level parallelism is one of the most common forms of parallelism being exploited by optimizing compilers and parallel machines. In the present study, the authors selected six large application programs and used an execution-driven simulation technique from MaxPar to identify and measure the effectiveness of concurrent DOACROSS loop execution. It was found that executing DOACROSS loops serially can significantly degrade the performance for some of the programs. The authors also measured and studied the characteristics of those cross-iteration dependences in DOACROSS loops and measured the capability of a state-of-the-art parallellizing compiler, KAP, in identifying and eliminating cross-iteration dependences.